Former Microsoft executive Kurt DelBene will take over the volunteer job of overseeing ongoing fixes to the federal Obamacare marketplace HealthCare.gov starting Wednesday, officials said.

DelBene is replacing management guru Jeffrey Zients, who was tapped by President Obama in October to manage the emergency repair job on that then-badly crippled website.

The switch comes at a critical time for HealthCare.gov, which has seen dramatic performance improvements under Zients. The site, which had very low enrollment levels in the first two months of operation because its tech troubles, now is engaged in a furious effort to sign up as many people as possible in new Affordable Care Act insurance by the New Year

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Kurt DelBene

DelBene, who retired last summer as president of the Microsoft Office division after two decades at the software behemoth, is the husband of US Rep. Suzan DelBene, (D-Wash), a fellow ex-Microsoft executive who was elected to Congress in 2012. Before Microsoft, DelBene was a management consultant with McKinsey and Company, and a software developer and systems engineer for AT&T Bell Laboratories.

Officials said DelBene has agreed to stay on the job of managing HealthCare.gov for at least the first half of 2014, which would include the March 31 deadline for open enrollment on that and other Obamacare exchanges.

Although he will be paid for his work, DelBene plans on returning all of that money to the US Treasury, the White House said.

Zients was originally scheduled to start his new job as director for the National Economic Council at the beginning of 2014. But on Tuesday it was disclosed that Zients will take that job after the State of the Union address on Jan. 28. In the meantime, Gene Sperling will stay on as council director until Zients takes over.

"I am pleased to announce Kurt Del Bene as my Senior Advisor and successor to Jeff Zients," said Kathleen Sebelius, secretary for Health and Human Services in a blog post on HHS's site on Tuesday.

Sebelius said, "The President and I believe strongly in having one person, with strong experience and expertise in management and execution, who is thinking 24/7 about HealthCare.gov. "

She lauded Zients for doing "an outstanding job working with our team to provide management advice and counsel on the HealthCare.gov project," saying the site now "is night and day from what it was when it launched on October 1."

"I am very grateful for his service and leadership."

Sebelius said DelBene "will be a tremendous asset in our work" because of his "proven expertise in heading large, complex technology teams and in product development."

She also said his responsibilities, while similar to those of Zients, will reflect the fact that the site has improved in recent months.

DelBene will "provide management expertise, operations oversight, and critical advice on additional enrollment channels, field operations, marketing and communication." He also "will execute the plan in place, so that we can ensure the site's performance is strong through the close of open enrollment on March 31,2014," Sebelius said.

"This will include a focus on increasing system stability, redundancy and capacity, and building on improvements to the user interface, while continuing to prioritize security and privacy issues in line with industry best practices."

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Jeffrey Zients

DelBene's wife, Rep. DelBene, in a statement said, "I'm pleased that the President has appointed Kurt to help oversee the continued improvement and implementation of the federal HealthCare.gov website website.

"The fact remains that there are millions of Americans who do not have access to affordable, quality healthcare today. To change that, it's critically important that HealthCare.gov works as it was supposed to."

"With his long career in the private sector, Kurt has the unique combination of skills and experience as an executive in the technology industry to manage a project the size and scope of HealthCare.gov," Rep. DelBene said. "I've long said that we need more people to enter public service who are focused on delivering results. Kurt has demonstrated throughout his career that he is about results, and his decision to join the Administration will be extremely valuable to their efforts to improve the website."

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Healthcare.gov

Kurt DelBene also won praise from his former bosses at Microsoft, including company founder Bill Gates.

"Kurt is a talented and capable executive, with a track record of successfully managing complex large-scale technology projects," Gates said. "Working with Kurt over many years, I know him to be a passionate advocate for using technology to solve difficult problems at scale. He brings deep expertise as a manager and engineer to his new responsibilities. I'm certain he'll make an important positive contribution in his new role with HHS."

Microsoft CEO Steve Ballmer said "Kurt's a phenomenal leader who established Microsoft Office as a world-class service for billions of people. Clearly, Kurt's technical and business skills will be invaluable in his new endeavor."

When DelBene takes over on Wednesday, he will be facing a less dire situation than the one Zients had to deal with after his appointment in late October.

Nearly two months of widespread software and hardware fixes made by government workers and private contractors during Zients' tenure at HealthCare.gov have left the site functioning much better than it had been after its botched Oct. 1 launch, with quicker load times and a sharply reduced error rate.

But it still needs to process what officials predict will be several millions enrollments in coming months. And the construction of a back-end system that handles critical financial transactions for insurers who sell plans on the site has been repeatedly postponed because of the frantic rush to fix the consumer interface.

Although enrollment on HealthCare.gov has greatly increased after the site was essentially relaunched at the beginning of December a slew of upgrades the pace of sign-ups is believed to still be well below the rate needed to hit 7 million enrollees nationwide by the close of enrollment in March, the target set by Obama officials.

For coverage that would begin Jan. 1, consumers have until next Monday to enroll in insurance bought through either the federal or state-run Obamacare exchanges.